The invention relates to a speed control device of sewing machines. It is an object of the invention to provide a control device installed outside of the sewing machine such as a foot step system, which may perform the control without having electric conduction, and therefore does not require any of insulating measures nor causes the electric shock, and which is simple in structure, light in weight and small in scale.
The existing controllers of the sewing machine are many of the foot step systems, and the structures thereof switch the resistance value within the controller, or slide it to effect the resistance control or electronic control so as to change the speed of the machine motor. Even in a case of changing the resistance in the electronic control and so far as a commercial power source is not separated by such as the insulating transformer, the foot step system control device needs the insulating measure suitable to the commercial electric power source, since the controller receives an electric potential of the power source. Therefore the controller is large scaled and there happens the electric shock if the insulation is not sufficient.